(1) Field of the Invention
The present invention relates to a polymer composition having excellent radiation sensitivity, which is a precursor of a heat-resistant polymer.
(2) Description of the Prior Art
As the polyimide precursor composition having a radiation sensitivity, especially a light sensitivity, the following compositions developed for the formation of insulating layers or passivation layers of semiconductors are known.
(a) A composition comprising a polyamide acid and 1 to 5% by weight of a dichromate (see, for example, U.S. Pat. No. 3,623,870). PA1 (b) A polyimide precursor composition in which a light-sensitive group has been introduced through an ester group having a structure represented by the following formula (see, for example, U.S. Pat. No. 3,957,512 and U.S. Pat. No. 4,040,831): ##STR2## (c) A composition comprising a polyamide acid and a compound having a carbon-to-carbon double bond and an amino group or quaternary salt thereof, which is dimerizable or polymerizable with radiation (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 54-145,794). PA1 (1) a polymer [I] containing repeating units represented by the following formula (A): ##STR3## wherein R.sup.1 is a trivalent or tetravalent aromatic or heteroaromatic residue having 6 to 30 carbon atoms, R.sup.2 is a divalent aromatic or heteroaromatic residue having 6 to 30 carbon atoms, R.sup.3 is a hydrogen atom or an ammonium ion, and n is an integer of 1 or 2, and COOR.sup.3 is located in an ortho or peri position with respect to the amide linkage, PA1 (2) an organic compound [II] having a radiation-dimerizable or radiation-polymerizable olefinic double bond and an amino radical or a quaternary ammonium salt, and PA1 (3) an aromatic monoazide compound [III] having no substituent or having a neutral or acidic substituent; and having 6 to 30 carbon atoms.
According to each of these conventional techniques, a varnish formed by dissolving a composition as described above into an appropriate organic solvent is coated and dried on a substrate to form a coating film, and the film is then irradiated with ultraviolet rays through an appropriate photomask and subjected to developing and rinsing treatments to obtain an intended relief pattern.
A patterned film of a polyimide precursor is subjected to an appropriate heat treatment to convert it to a polyimide film having a heat resistance.
Although these conventional compositions are advantageous in that patterning can be accomplished directly by irradiation with light, they are still insufficient. For example, the composition (a) has a poor stability, and the composition (a) must be used just after the polyamide acid is mixed with dichromic acid; considerably limiting industrial utilization. Furthermore, in case of the composition (a), since inorganic ions are present in the patterned film formed from this composition, the patterned film cannot be used in the field of semiconductors, where the reliability of such devices is seriously influenced by the presence of the inorganic ions.
In the composition (b), the constituent polymer is formed mainly by reacting a compound having a photosensitive group and a dibasic acid chloride group with a diamine, and the steps of forming this polymer are complicated. Furthermore, since the chlorine ion generated by dehydrochlorination is left in the film, there is a risk that possible adverse effects arising from the presence of the chlorine ion will deteriorate the reliability of the semiconductor devices.
In the composition (c), the foregoing defects are moderated, but the sensitivity is so low that an exposure quantity as large as several hundred mJ/cm.sup.2 is necessary and, hence, the composition cannot be treated sufficiently by a light exposure apparatus customarily used in the semiconductor industry.